Mitx addition/cg/gunicorn conf

It wasn't quite a clean merge, but it does work and fixes a bunch of our gunicorn <-> nginx issues. @bdero if you could take a look and maybe test against a sandbox.
Just grabbed from a cherry-pick, from reading https://github.com/edx/configuration/blob/master/playbooks/roles/edxapp/defaults/main.yml there is no consistency